1. Field of the Invention
The present invention relates to a mounting arrangement for a temperature sensor for a centrifuge instrument.
2. Description of the Prior Art
A centrifuge instrument is an apparatus adapted to separate the components of a sample. To accomplish this end the sample is introduced into one of a plurality of sample receiving cavities disposed in an element called a rotor. The rotor is mounted on the upper end of a shaft that projects upwardly into a chamber or bowl that is supported on the interior of the housing of the centrifuge instrument. The shaft is connected to a motive source which, when activated, rotates the rotor to a predetermined rotational speed. Centrifugal force acts on the sample carried within the cavity and causes the components thereof to separate in accordance with their density.
It is frequently desirable to spin the sample at a specific regulated temperature. For this purpose the centrifuge chamber is refrigerated, as by the provision of refrigeration coils on the exterior of the chamber. The temperature of the rotor and, therefore, the temperature of the sample carried therein is monitored by a temperature sensor which forms a component of a temperature control system.
In some prior art instruments such as that disclosed in U.S. Pat. No. 3,409,212 (Durland et al.), an infrared radiometer is used as a temperature sensor to measure the energy emitted from the rotor. As is exemplified by this patent the sensor is mounted in a position vertically beneath the rotor. The sensor is operative to detect energy radiating from the undersurface of the rotor and to provide a signal representative of the temperature thereof.
Another known temperature sensing arrangement for a centrifuge instrument physically mounts the sensor in the sidewall of the chamber. A sensor so mounted serves to provide an indication of the temperature of the chamber sidewall. Exemplary of such an arrangement is that contained in the centrifuge instrument sold by E.I. Du Pont de Nemours and Company as the OTD Series ultraspeed centrifuge instruments. These instruments also have a floor mounted radiometer for measuring heat radiated from the bottom of the rotor. The instruments sold by E.I. Du Pont de Nemours & Co., Inc. as the RC-Ultra Series also include a floor mounted radiometer. The instruments also manufactured and sold by the same manufacturer as the RC-5C and the RT-6000 also have floor mounted temperature sensors to measure the chamber floor temperature and/or chamber air temperature.
Mounting the sensor on the sidewall or the floor of the chamber presents an obstruction on these surfaces that interferes with the cleaning of the chamber and that creates air turbulence which adds rotational drag to the rotor and, thus, heat to the system if the rotor is rotated in a nonevacuated environment. This is viewed as disadvantageous.
A mounting arrangement which disposes the temperature sensor on the floor of the chamber may be viewed as disadvantageous for another reason. Such a mounting location for the temperature sensor exposes the same to a relatively high temperature thermal mass in the form of the motive source which is usually mounted directly below the chamber. Exposure to this potential heat source could deleteriously affect the accuracy of the temperature reading provided by the sensor.
It is also noted that a system which mounts a radiation responsive form of temperature sensor to the floor of the chamber of necessity utilizes the bottom surface of the rotor as the radiating surface from which the temperature of the rotor element may be detected. The radiated energy measured by the sensor is a function of the emissivity of the surface at which it is directed. Because the bottom of the rotor is particularly susceptible to damage and wear during normal handling, this surface may become scratched. The imperfections in this surface adversely affect the emissivity of that surface and therefore the accuracy of any temperature measurement based thereon.
In view of the foregoing it is accordingly believed advantageous to provide a support arrangement for a temperature sensor in a centrifuge instrument which does not create additional turbulence, does not expose the sensor to the possibility of erroneous readings due to proximity to other thermal sources, and does not rely upon the emissivity of the bottom surface of the rotor as the surface from which the temperature measurements are made.